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Office of Ground Water and Drinking Water 

November 4, 2013 

MEMORANDUM 

SUBJECT: Basis for Expedited Approval of Hach Company Method 10260: Determination of 

Chlorinated Oxidants (Free and Total) in Water using Disposable Planar Reagent-Filled Cuvettes and 

Mesofluidic Channel Colorimetry 

FROM: Glynda Smith, Chemist, SRMD/TSC 

 Steve Wendelken, Chemist, SRMD/TSC 

TO: The Record 

Hach Company’s disposable Planar Reagent-Filled Cuvette (PRFC) method measures free, total and 

combined chlorine as an optional alternate test procedure to Standard Method 4500-Cl G which is 

approved in the national primary drinking water regulations at 40 CFR 141.74(a)(2) for determination of 

free and total chlorine, and at 40 CFR 141.131(c)(1) for determination of free, total, and combined 

chlorine. 

An automated instrument draws a water sample into a cuvette that is prefilled with the reagents that 

are required to perform DPD (N,N-diethyl-p-phenylenediamine) colorimetric chlorine tests. Automation 

of the DPD determination relative to the manual procedure described in the approved method reduces 

errors associated with reagent addition, mixing and color development. 

Three laboratories participated in a multi-laboratory validation study. The laboratories evaluated 

precision and accuracy in a variety of drinking water matrices (e.g., low ionic strength, high ionic 

strength, and tap water samples drawn from both surface water and ground water sources). MDLs were 

determined for free chlorine and for total chlorine. Accuracy and precision were evaluated in all test 

matrices by fortifying replicates at 2.0 mg Cl2/L. The Hach PRFC method was evaluated side by side with 

the approved method, Standard Method 4500-Cl G, which employs DPD solid reagents. The complete 

data summary is provided in the Hach ATP Validation Report. Briefly, the results are as follows: 

 

Free Chlorine 

 The PRFC method the approved manual DPD method yielded the same MDLs (0.019 mg/L) in 

low ionic strength water. In high ionic strength water, the PRFC method yielded a pooled MDL 

of 0.025 mg/L and the approved DPD method a pooled MDL of 0.020 mg/L. 

 The pooled average recovery in low ionic strength water fortified at 2 mg/L free chlorine was 

103% for the results obtained with the PRFC method relative to the approved manual DPD 

method and 102% in high ionic strength water fortified at 2 mg/L free chlorine. 

 The pooled average recovery for all matrices fortified at 2 mg/L free chlorine was 103.9% for the 

PRFC method relative to the approved manual DPD method (based on 120 tap water samples 

drawn from ground water and surface water sources covering a pH range of 6.0 to 8.8). 

 The interference in the free chlorine determination from a 2.0 mg/L monochloramine standard 

was determined to be 6.3% in the PRFC method and 4.0% with the approved manual DPD 

method. 
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Total Chlorine

 In low ionic strength water, the PRFC method yielded a pooled MDL of 0.025 mg/L compared to 

the approved manual DPD method which had a pooled MDL of 0.050 mg/L. In high ionic 

strength water, the pooled MDL for the PRFC method was 0.033 mg/L and the approved manual 

DPD method was 0.040 mg/L.

 The pooled average recovery in low ionic strength water fortified at 2 mg/L total chlorine was 

93% for the results obtained with the PRFC method relative to the approved manual DPD 

method and 92% in high ionic strength water fortified at 2 mg/L total chlorine.

 The pooled average recovery for all matrices fortified at 2 mg/L total chlorine was 96.5% for the 

PRFC method relative to the approved manual DPD method (based on 114 tap water samples 

drawn from ground water and surface water sources covering a pH range of 6.0 to 8.8).

Based on evaluation of the accuracy, precision and sensitivity determined in the multi-laboratory 

validation study, the Hach PRFC method is equally as effective as Standard Method 4500-Cl G in 

determining free, combined, and total chlorine in drinking water.